1. Field of the Invention
This invention relates to a process of converting ethylbenzene to styrene by catalytic dehydrogenation at temperatures of about 600.degree. C. in the presence of water vapor in a tubular reactor.
2. Discussion of the Prior Art
It is known to convert ethyl benzene to styrene by catalytic dehydrogenation in the presence of water vapor at temperatures of 560.degree. to about 600.degree. C. In the processes which have been commercially adopted and are carried out in a gas-fired tubular reactor or in an adiabatic shaft furnace reactor or in an annular cracking reactor, an economically satisfactory conversion can be effected only in conjunction with poor selectivities and high steam supply rates.
In a gas-fired tubular reactor, a conversion of about 40 mole percent is usually achieved. Apart from the low conversion, that process has the disadvantage that it involves a high heat consumption caused by the circulation of hot gases in large quantities, so that energy is required at a high rate, and that the hot gas entering the tubular reactor must be at a high temperature of about 700.degree. C.
It is also known to convert ethylbenzene to styrene by adiabatic dehydrogenation. In that case the heat required for the reaction must be supplied by a feeding of hot water vapor at a high rate. To effect an economically satisfactory conversion, the dehydrogenation is effected in two stages and the mixed reactants must be reheated before entering the second reactor. In that process the temperature of the mixture must not rise substantially above 630.degree. C. because the ethylbenzene may otherwise be cracked. On the other hand, the temperature must not decrease below 565.degree. C. because the reaction rate would otherwise decrease strongly (Chemi-Ing.Techn. 37, No. 4 (1965), pp. 361-367).
A disadvantage of that process resides in that more water vapor is required than in the process using a tubular reactor. For instance, if preheating is effected to a temperature of 500.degree. C., about 2.3 kg of water vapor at a temperature of about 710.degree. C. and a pressure of about 7 to 10 bars will be required per kg of ethylbenzene. Besides, as a result of the cracking reactions the yield of styrene is lower than where a tubular reactor is used. Another disadvantage resides in that the reaction product obtained by the adiabatic process contains twice as much water vapor so that larger cooling means are required for the condensation.